<!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8">
    <title>Document</title>
  </head>
  <body>
    <input type="text">
    <script>
      var search = document.querySelector('input');
      document.addEventListener('keyup', function (e) {
        if (e.keyCode === 83) {
          search.focus();
        }
      });
    </script>
  </body>
</html>